title: Plasmid-encoded lysine decarboxylation in Proteus morganii.
abstract: As a rule, Proteus morganii does not decarboxylate lysine. However, lysine-positive P. morganii strains have been recently described. We suspected a plasmid origin for this atypical character, and we analyzed 14 strains to study this question. Among these strains, 8 yielded lysine-negative segregants after acridine orange or ethidium bromide treatment, and 10 transferred their lysine-positive character to a recipient P. morganii strain. All of the 14 strains analyzed at least segregated or conjugated. Three lysine-positive transconjugants, in turn, segregated lysine-negative variants after ethidium bromide treatment. The eight wild-type lysine-positive strains that segregated lysine-negative subclones contained a large (35 to 45 megadaltons) plasmid detectable by agarose gel electrophoresis. Similarly, the 10 lysine-positive transconjugants contained a plasmid of the same size, whereas P. morganii 1000, the recipient strain, did not contain any detectable plasmid. The large plasmid clearly disappeared in 9 of 11 lysine-negative segregants analyzed. It is concluded that the lysine-positive character of these P. morganii strains is plasmid encoded, and the taxonomical implications are discussed.
mesh_terms: D002262:Carboxy-Lyases / Q000235:genetics*; D003227:Conjugation, Genetic; D003653:Decarboxylation; D008239:Lysine / Q000378:metabolism*; D010957:Plasmids; D011511:Proteus / Q000235:genetics* / Q000378:metabolism
chemical_list: D002262:Carboxy-Lyases; C021520:lysine decarboxylase; D008239:Lysine